Method of reducing rolling mill roll wear

ABSTRACT

A method of reducing the wear in the work rolls of a mill stand for rolling a workpiece which comprises applying a lubricant onto the surface of the rolls in carefully controlled quantities during the rolling process.

United States Patent [1 1 Hostetter et a1. 7,

[ METHOD OF REDUCING ROLLING MILL ROLL WEAR [7 5] Inventors: Richard S. Hostetter; Mahesh M. Vyas, both of Bethlehem, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: Mar. 7, 1973 [21] Appl. No.: 338,711

[52] US. Cl. 72/45, 72/236 [51] Int. Cl B2lb 45/02, B2lb 27/10 [58] Field of Search 72/41-45, 200, 72/201, 202, 236, 364

[5 6] References Cited UNITED STATES PATENTS 3,150,548 9/1964 Roberts 72743 3,208,253 9/1965 Roberts 72/21 3,523,437 8/1970 Bales et al. 72/43 Apr. 16, 1974 3,605,473 9/1971 Lyon et a1 72/201 3,648,497 3/1972 Long et al 72/21 3,656,330 4/1972 Brown et al. 72/45 X 3,709,012 1/1973 Larsonneor 72/43 X 3,763,679 10/1973 Lane et a1 72/45 OTHER PUBLICATIONS High Temperature Rolling, M. R. Edmundson, Iron & Steel Yearbook, 1970, pp. 522-525.

A New High-Temperature Lubricant for Hot Rolling," A. R. Globus, Iron & Steel Engineer, Aug. 1970, pp. 93-94.

Primary Examiner-Charles W. Lanham Assistant Examiner-E. M. Combs [5 7] ABSTRACT A method of reducing the wear in the work rolls of a mill stand for rolling a workpiece which comprises applying a lubricant onto the surface of the rolls in carefully controlled quantities during the rolling process.

11 Claims, 6 Drawing Figures PATENTED APR 18 1974 SHEEI 1 0f 3 E L Z n N 6 w M M n m m m SHEET 3 OF 3 0 BRA/VD -/VE/7T :1 5mm: A Warm/0. x ammo 5 NEAT o flaw/v0 5 WATER/OIL A ammo C WATER/OIL film/v0 0 Warm/0a.

BRANDS A8 C ARE SYNTHETIC ESTER O/LS BRANDS B80 ARE FATTY a/Ls 5L IPPA GE ROLL 4 OER/CANT APPL /cn 7/0/VKA7'E, 0/5 f2 0F x04 1. 0 suxrqcs x /0' 4 METHOD OF REDUCING ROLLING MILL ROLL WEAR BACKGROUND OF THE. INVENTION Industries dependent upon rolling mills as a step in a manufacturing process, as e.g., the steel and aluminum industries, have been constantly searching for means to reduce the wear on the rolls. The economic factor is obvious. Reduced wear on the rolls results in increased roll life, thus fewer roll changes are required which results in an increase in mill production. In addition; savings are realized from fewer roll redressings and reduced roll inventory requirements.

' ods of applying lubricant to the surfaces of the rolls have been popular: v

1. the lubricant is applied to the rolls in neat form,

2. lubricant is introduced into the roll'cooling water and is sprayed on the roll surface through the roll cooling system, and I t 3. water and lubricant are mixed in predetermined proportions and applied to the rolls through a spray header which is separate from the roll cooling system.

The lubricants are expensive and it is therefore important to carefully control the amount of lubricant supplied to the surface of the rolls to avoid waste.

It is an object of this invention to provide an economical and efficient method of reducing the wear in the rolls of a mill stand adapted for rolling a workpiece.

It is a further object of the invention to provide a method for applying a lubricant onto the surface of the rolls of a mill stand.

It.is still another object of the invention to provide a method forcontrolling the quantity of lubricant applied to the surface of the rolls of a mill stand.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side elevation of a mill stand for rolling a workpiece;

FIG. 2 is a schematic piping diagram for the application of lubricant to the rolls according to the invention;

FIG. 3 is a graph showing the relation between lubricant quantity and application rate for different strip velocities;

FIG. 4 is a graph showing the relation between quantity of lubricant and mixture pressure for different water/oil concentrations;

FIG. 5 is a graph showing therelation between roll wear reduction and lubricant application rate; and

FIG. 6 is an elevational view of the rolls of a universal mill incorporating the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The most effective means for the application of a controlled amount of a lubricant to the surfaces of the rolls in a mill stand adapted for rolling a workpiece has been found tobe the method in which a water-oil mixture in predetermined proportions is applied to the roll surface through a spray header which is separate from the roll cooling system. The invention as hereinafter described will, therefore, be'directed to this specific means of application. It will be understood by those skilled in the art that there are other means for applying lubricants onto the surface of rolls according to this invention.

The lubricants which are considered to be effective for reducing the wear in the rolls of rolling mills include synthetic ester oils, developed especially for hot mill use. Fatty oils, cold mill lubricants, have also been found to be very effective. The fatty oils include palm oil. There is no significant difference in the wear reduction obtained using these different lubricants. The cost of the material and system maintenance, therefore, determined the most economical lubricant to use.

The fatty oils, e.g., palm oil, are semi-solids at room temperature and so must be heated to l30l40 F. in order to flow through the pipe lines. When used as a mixture with water,'the water should also be heated to l40-l80 F., otherwise the oil will not mix satisfactorily with the water but will congeal and clog the spray nozzles.

The hot mill lubricants should also be heated to about F. to facilitate pumping, but if necessary can be dispersed in cold water without producing nozzle clogging problems.

Clogging of the spray nozzles is a major problem with the neat oil application. Only small quantities of oil are needed for roll lubrication regardless of the method of application and therefore the diameter of the nozzle orifice can be quite small, as e.g., 0.026 in. However, the spray nozzles of such small diameter clog readily and result in an inefficient system.

Since a mixture of oil and water provides a greater flow volume for the same quantity of oil, the spraying of a water-oil mixture permits the use of larger diameter nozzle orifices. Commercially available nozzles with a 0.062 in. diameter orifice have been found to be efficient..

The mill stand 10 as seen in FIG. 1 is exemplary of one type of rolling mill apparatus to which the instant invention is applicable. The mill stand 10 comprises top backup roll 11 and bottom backup roll 12, work rolls 13, top spray header 14 and bottom spray header 15. Wipers 16 of felt and/or rubber are mounted in a manner that will wipe the water off the roll surface before the lubricant is sprayed on the rolls to insure that the lubricant comes in contact with and adheres to the roll surface. Separate means (not shown) for flooding the rolls with a cascade of coolant to cool the rolls is provided. Coolant is supplied to the rolls in accordance with standard mill practices.

Referring now to FIG. 2, a schematic diagram of the preferred system for applying lubricant through a system of spray headers is seen. Predetermined proportions of oil and water are supplied to mixing nozzle 20 and thence by feeder lines 21, 22, and 23 to spray headers 14 and 15 and the nozzles 17 mounted thereon.

The concentration of oil in the mixture is the same for top and bottom sprays. However, it has been found that the bottom roll frequently experiences more wear and therefore requires more oil than the top roll. Additional oil is'applied to the bottom roll by using more nozzle in the bottom spray header than in the top spray header thereby applying the greater volume of wateroil mixture to the bottom roll. FIG. 2 is seen to have five spray nozzles for the bottom roll and four spray nozzles for the top roll with solenoid valves provided to cut out the end sprays when a narrow workpiece is being processed. The oil application rate may be controlled from a remote panel (not shown) any from the mill stand or manually, varying the concentration of oil backup rolls. 1

The most effective location for the application of the lubricant or water-oil mixture is on the backup rolls on the entry side of the mill stand. Occasionally, however, it may be necessary because of physical limitations to locate the bottom spray header on the delivery side of the mill. This location will have no adverse effect on the lubricant application to the bottom work roll as long as means is provided to deflect the cascading coolant away from the bottom backup roll 12 ahead of the point where the spray headers 15 apply a water-oil mixture to the roll surface.

This invention defines the effective working range of the lubricant application rate to obtain the greatest reduction in roll wear without causing mill operating problems such as slippage. The lubricant application rate is defined in terms of lbs of oil/sq ft of rolled surface or the equivalent lbs of oil/ sq ft of roll surface in contact with the workpiece. For example, in the rolling of sheet between two rolls, the roll surface in contact with the workpiece is equal 'to the width of the work- 'piece times the circumference of the rolls times the number of revolutions of the rolls during the rolling ofthe sheet. It has been found that the reduction in roll wear is relatively constant between lubricant application rates of 0.0003 and 0.0008 lb/sq ft of roll surface in contact with the workpiece. See FIG. 5. As seen in the graph of FIG. 5, lubricant application rates below 0.0003 lb/sq ft of roll surface in contact with the workpiece result in a decrease in roll wear reduction. Lubri The concentration of oil in the water-oil mixture may vary from about 2.5 to 15 percent by volume for different stands in a rolling mill but the solution concentration is the same for top and bottom sprays of the same stand. Within the effective working range of lubricant application referred to hereinabove the rate of 0.00055 lb of oil/sq ft of roll surface in contact with the workpiece has been found to be most effective. Oil is mixed with water and sprayed only for the part of the time that the workpiece is in the mill. Mixture pressure is governed by water pressure, which should be approximately 40-50 psig at the nozzles. Oil pressure should be 20 about 20 psig higher than the water pressure to assure thorough mixing with the water.

The following procedure is used to determine the lubricant application rate for the reduction of roll wear in the rolls of a hot strip mill:

1. Select the number of nozzles to be used on the top and bottom headers according to the width of the material being rolled using the header assembly shown in FIG. 2.

2. Select the application rate from FIG. 3 knowing the strip velocity at the particular stand and the quantity of oil to be used per square foot of rolled surface. Experience has shown that 0.00055 lb/sq ft of rolled surface is a good starting number, but can be modified if desired.

3. Select the water-oil mixture concentration from Table 1, following, knowing the number of nozzles,

mixture nozzle pressure and mixture concentration.

This procedure is repeated for each stand to set the flow of oil and water on the remote control panel before the start of rolling. Since the effectiveness of the lubricant in reducing roll wear may not be the same for all mills, trial runs should be made to determine the most effective and economical lubricant application rate. Such rate will fall between about 0.0003 and about 0.0008 lb/sq ft of roll surface in contact with the workpiece.

Table 1 which follows augments the data given on .5195. .4 and TABLE 1.WATER AND OIL FLOW RATES USING RECOMMENDED NOZZLES AND PRESSURES Flow of oil and water stand Total flow g p ml mixture 5% oil 10% oil 16% oil 20% oil per stand,

g.p.m Water Oil Water Oil Water Oll Water 011 "Recommended operating range.

The following specific example following the procedure outlined above demonstrates the applicability of the invention to a hot strip mill:

The procedure for determining oil and water flows for any finishing stand of a hot strip mill is described below by making a case study of the second finishing stand (F-2) in a 56 in. hot strip mill:

a. The average width of the strip to be rolled is 36 inches. Therefore the number of nozzles to be activated according to FIG 2 wherein a typical spacing of nozzles is given is five, three on the bottom spray header 15 and two on the top spray header 14.

b. The recommended lubricant application rate is 0.00055 lb of oil/sq ft of rolled surface and the strip velocity is 560 ft/min. From FIG. 3 it is determined that the quantity of lubricant required is 0.025 lb/min/in of width. i

c. The mixture pressure at the nozzles is selected at 50 psig (Table 1) and the approximate concentration of oil desired from FIG. 4 is 8 percent.

d. From Table l the flow meter settings are read as follows: (interpolate between the 5 percent and 10 percent mixture values) Mixture flow 3.35 gpm Oil flow 0.27 gpm Water flow 3.08 gpm It is clear that charts can be readily calculated for application to mills of other types, as e.g., structural, plate, bar, etc. 1

In the development of this invention roll surface profiles were measured using a roll-profile measurement gage to determine the wear pattern for work rolls used with and without lubricant application. The results showed that the roll wear was reduced about 50 per-.

cent by the application of a lubricant and that there was no significant difference in the effectiveness of any of the lubricants evaluated for a given consumption rate. The time between work-roll changes is doubled and consequently the resulting reduction in mill down-time and increased roll life provide substantial savings in production costs.

FIG. 6, to which particular reference is now made, shows the instant invention applied to a universal mill for rolling structural shapes. It has been found that maximum roll wear occurs on the rolls of this type of mill on portions 30 of the surfaces of the rolls. It is necessary, therefore, to apply lubricant on universal mill stand roll surfaces at portions 30 only, at the rates of application hereinbefore disclosed by means of spray nozzles 17 as seen in FIG. 6. Because of the fragmentary nature of FIG. 6 the nozzles 17 are not seen on the top roll. Application to the remaining roll surface is unnecessary and wasteful.

It will be clearly understood by those skilled in the art that the selective application of lubricant to portions of the surfaces of the rolls of the rolling mill stand at the rate of between about 0.0003 and about 0.0008 lb/sq ft of the selected portions of the roll surface that is in contact with the workpiece will be effective for many types of rolling mills where the wear on the rolls is concentrated in particular areas.

The determination to remove rolls from the mill for redressing depends on the relative amount of wear of the roll surfaces between thearea of maximum wear and the wear on the rest of the roll surface. The instant invention reduces this wear by as much as 50 percent.

We claim:

1. A method of reducing wear in the rolls of a mill stand for rolling a workpiece comprising applying oil to the surface of the rolls and controlling the supply of oil to between about 0.0003 and about 0.0008 lb/sq ft of roll surface in contact with the workpiece.

2. A method as defined in claim 1 wherein the oil is applied by spray means. I

3. A method as defined in claim 1 wherein the supply of oil is about 0.00055 lb/sq ft of roll surface in contact with the workpiece.

4. A method as defined in claim 1 wherein the oil is mixed with water.

5. A method asdefined in claim 1 wherein the oil is mixed with water and applied by spray means.

6. The method as defined in claim 1 wherein the oil is applied to the surfaces of the back-up rolls of the mill.

7. The method as defined in claim 5 wherein the oil is applied to the back-up rolls on the entry side of the mill stand.

8. A method as defined in claim 1 wherein the oil is applied by spray means to the surfaces of the back-up rolls on the entry side of the mill stand.

9. A method of reducing the wear in the rolls of a mill stand for rolling a workpiece having work rolls and back-up rolls comprising spraying oil onto the surfaces of the back-up rolls on the entry side of the mill stand and controlling the supply of the oil to about 0.00055 lb/sq ft of roll surface in contact with the workpiece.

10. The method as defined in claim 9 wherein the oil is mixed with water.

111. A method of reducing wear in the rolls of a mill stand for rolling a workpiece comprising applying oil to the surface of selected portions of the rolls and controlling the supply of oil to between about 0.0003 and about 0.0008 lb/sq ft of surface of the selected portions in contact with the workpiece. I 

1. A method of reducing wear in the rolls of a mill stand for rolling a workpiece comprising applying oil to the surface of the rolls and controlling the supply of oil to between about 0.0003 and about 0.0008 lb/sq ft of roll surface in contact with the workpiece.
 2. A method as defined in claim 1 wherein the oil is applied by spray means.
 3. A method as defined in claim 1 wherein the supply of oil is about 0.00055 lb/sq ft of roll surface in contact with the workpiece.
 4. A method as defined in claim 1 wherein the oil is mixed with water.
 5. A method as defined in claim 1 wherein the oil is mixed with water and applied by spray means.
 6. The method as defined in claim 1 wherein the oil is applied to the surfaces of the back-up rolls of the mill.
 7. The method as defined in claim 5 wherein the oil is applied to the back-up rolls on the entry side of the mill stand.
 8. A method as defined in claim 1 wherein the oil is applied by spray means to the surfaces of the back-up rolls on the entry side of the mill stand.
 9. A method of reducing the wear in the rolls of a mill stand for rolling a workpiece having work rolls and back-up rolls comprising spraying oil onto the surfaces of the back-up rolls on the entry side of the mill stand and controlling the supply of the oil to about 0.00055 lb/sq ft of roll surface in contact with the workpiece.
 10. The method as defined in claim 9 wherein the oil is mixed with water.
 11. A method of reducing wear in the rolls of a mill stand for rolling a workpiece comprising applying oil to the surface of selected portions of the rolls and controlling the supply of oil to between about 0.0003 and about 0.0008 lb/sq ft of surface of the selected portions in contact with the workpiece. 